This study is designed to test the efficacy of tonsillectomy, and of tonsillectomy with adenoidectomy (T&A), in reducing the occurrence of episodes of throat infection in children with previous throat-infection experiences that conform to currently recommended and invoked criteria for tonsillectomy. Children with specified minimum and maximum histories of recurrent throat infection are recruited from among Children's Hospital outpatients and patients referred by community physicians or brought directly by parents. After evaluation, children found to be eligible for the study are offered random assignment to one of three treatment groups: tonsillectomy, T&A, or nonsurgical control. All subjects are examined at six-week intervals, and also for intervening respiratory or related illness. Telephone calls are made bi-weekly to inquire about a specified group of symptoms and events. The principal end-points are the frequency and severity of episodes of throat infection, but other measures of morbidity also will be analyzed. To date 1367 children have been evaluated, and 141 children have been randomly assigned to one of the three treatment groups. Preliminary data show no differences in outcome between tonsillectomy and T&A, but show statistically significant differences in outcome favoring surgical treatment (tonsillectomy or T&A) over nonsurgical treatment during the first follow-up year, and trends favoring surgery during the second follow-up year. However, the magnitude of the differences between surgical and control subjects appears less than in our earlier trial involving more severely affected children. In particular, control subjects have developed few episodes rated as moderate or severe; virtually all of their episodes have been mild. Thus the benefit of surgery in these subjects may fall short of justifying the risks and costs. If these results continue with larger numbers of subjects over longer periods, it may be possible to conclude (1) that adenoidectomy should not be added to tonsillectomy as a matter of routine, and (2) that current, generally accepted standards regarding indications for tonsillectomy on the basis of recurrent throat infection are not sufficiently stringent, and should be modified or at least sharply qualified. Enrollment of subjects through August 1986 and follow-up through August, 1989 appears necessary to achieve results sufficiently conclusive to be persuasive to clinicians and to influence well-established standards of practice.